1. Field of the Invention
This invention relates to an electronic target detecting device (TDD) and more particularly to a reaction-type pulse Doppler TDD.
2. Description of the Prior Art
Electronic proximity TDD's for explosive missiles usually comprise a miniature radio frequency transmitter-receiver of the radiating-detector type which emits continuous radio frequency waves from an antenna carried by the missile, or a separate radio frequency oscillator and detector coupled to the antenna. As the missile approaches the target, some of the TDD radiation is reflected by the target and received by the TDD through the antenna in a continuously varying phase relationship to that transmitted. The effect of this changing phase difference on the radiating-detector or the diode detector of the radio frequency oscillator and diode detector combination is the generation of an audio frequency voltage in the transmitter-receiver. This voltage is of Doppler frequency and is amplified by a selective audio frequency amplifier of the TDD to initiate a firing circuit when the amplitude and frequency of the reflected radiation reaches a predetermined level at a desired distance from missile to target. The firing circuit in turn functions an electric squib in its circuit to cause detonation of the explosive payload.
TDD's of the above described type are susceptibly to jamming, particularly to repeater method of jamming in which some of the r-f energy radiated by the fuze is picked up by a receiving antenna, greatly amplified and reradiated. The phase of this reradiated signal compared to that of the original signal radiated by the TDD varies with the distance from TDD to repeater and this gives rise to a Doppler shift of the jamming signal frequency, which usually will result in near optimum TDD amplifier response.